pkg/codesearch: reduce memory consumption when building index

With all references in the index, it become quite big.
Merge and dedup the resulting index on the fly.
Also intern all strings b/c there are tons of duplicates.

This also removes unnecessary duplicates (effectively ODR violations in the kernel)
due to use of BUILD_BUG_ON. The macro produces different function calls
in different translations units, so the same function may contain
__compiletime_assert_N1 call in one TU and __compiletime_assert_N2 in another.

Over this reduces resource consumption of index building from:
time:296.11s user:16993.71s sys:6661.03s memory:82707MB
to:
time:194.28s user:16860.01s sys:6647.01s memory: 3243MB

25x reduction in memory consumption.

0 files changed, 0 insertions, 0 deletions